Automatic telephone-repeater.



W. A. LONG.

AUTOMATIC TELEPHONE REPEATERL APPLICATION FILED JUNE27. 1912. RENEWED FEB. 1,1913.

Patented Jan. 21, 1919.

mar m N W/TNESfiES WJA. LONG., AUTOMATIC TELEPHONE REPEATER APPLICATION FILED JUNK-I27, l9l2- RENEWED-FEB. 1.1918.

2 SHEETSSHEET 2.

Patented Jan. 21, 1919.

WITNESSES ran STATES PATENT OFFICE.

WILLIAM A. LONG. OF SIOUX CITY, IOWA, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE-REPEATER.

Specification of Letters Patent.

Patented Jan. 21, 1919.

Application filed June 27, 1912, Serial No. 706 199. Renewed February 1, 1918. Serial No. 214,985.

To n66 who). it may concern Be it known that I, WILLIAM A. Lose, a citizen of the United States of America, and resident of Sioux City, \Voodbury county, Iowa, have invented certain new and useful Improvements in Automatic Telephone-Repeaters. of which the following is a specification My invention relates to automatic telephone repeaters for use in connection with automatic telephone systems. It relates .nore specificallyto what are known as threewire to two-wire repeaters-that is, repeaters which are included in the trunk lines vertical and rotary impulses which are de- 9 livered to the line by the calling device of a thrcewire substation, and must. trans form these impulses into impulseswhich are transmitted over the two sides of thetrunk line in series. In the operation of such a system, when the substation calling device is operated to call any digit after the connection has been extended to the repeater. a number of ground impulses corresponding to the digit called are transmitted through the vertical line relay ot' the repeater. This line relay then operates in response to these impulses to cause the bridge across the twowire trunk line to be opened :1 corresponding number of times In threewire systems as ordinarily constructed the calling s.':l):;criber. in order to ring; the called subscriber after connection has been completed. is required to depress =1 butto at his telephone in order to ground the vertical side of the line. This ground will be maintained as lone as the subscriber continues to press this ringing button. This prolonged grounding of the vertical line would tend to maintain the bridge across the two-wire trunk open tor a corresponding length of time. if this bridge were maintained open for this period 0 time. the switches of an ordinary two-wire system would be released. As a subscriber cannot be supposed to know whether he is calling another three-wire subscriber'or calling a two-Wire subscriber, it becomes necessary to provide means whereby when a subscriber grounds his vertical line in order to ring, as he supposes, a subscriber, the switches at the two-wire exchange will not be released.

An object of my invention to provide a repeater which is so arranged that the momentary grounding of the vertical line at. the substation, while the. impulses corresponding to the various digits of the called number are being transmitted, will momentarily open a bridge across the twowire trunk a corresponding number-of times in order to operate the two-wire switches. but the prolonged groundingof the vertical line will not open the bridge across this trunk acorresponding length of time. but will .merely momentarily open the bridge, which is not sufiicient. to cause the release of these two-wire switches.

A further object of my invention is the general improved construction and operation of a repeater.

My invention will be more readily understood by reference to the accompanying drawings. in which I have illustrated a system in which mv improved repeater is employed.

In the accompanying drawings Figs. 1 and 2 taken together show a complete connection betweenia calling substation A and a called substation A in-. an automatic telephone system embodying the principles of my invention.

The system herein represented is of the well-known type of system employing subscribers individual or preselector switches, group selectors and connectors. The apparatus shown in Fig. 1 is of the type generally known as three-wire. The apparatus shown in Fig. 2 is of the type generally known as two-wire. The apparatus shown in Figs. 1 Mid 2 may be either in the same or (lifter-cut exchanges. The connection shown extends from the calling substation A through its individual line switch C, the first selector E. the repeater F, the selector H and the connector I to the line of the called substation A. For the purpose of furnishing current for operating the central oz'iice apparatus. a

are

6;; aeneeo of impulse springs 7 and 8 and a toothed impulse wheel 6, which latter is controlled by the subscriber through the medium of a dial (not shown) provided with finger holes. Such a calling device is well known in the art and it not thought necessary to give a detailed description of the same herein.

As well known, when a calling subscriber rotates the dial of a calling device of this character preparatory to calling any digit, the so-called rotary impulse spring 8 is forced into contact with the ground post 10 once... Then as the dial and impulse wheel 'retu .1 to normal position after being rcleas: by the subscriber, the so-called vcrtical mini .3 spring 7 is forced into' contact with the round post 10 a number of times, corresponding to the digit called, after whicl'i the rotary impulse spring 8 is once more grounded. The substation A is also provided with a push button. 11 which, when depressed, opens the bridge across the line through the secondary winding of the induction coil and the receiver and connects one side of the line to ground.

The subscribefs individual switch C. its master switch D and the selector E are of the well-known type of central oilice switching apparatus disclosed in British patent to 1%. i James. llo. 26,301 of 1906. and in the Western ZiZccf rkri'a n of Chicago, Illinois. of January l1, l8 and of 1908. The construction of the selector E is also disclosed in United States Letters Patent No. 815,321. granted March 13, 1906, to Keith, Erickson a l Erickson. As shown herein, the selec- 1 comprises the usual line and private wipers 12, 13 and l lwhich are carried by a shalt (not shown) having a vertical motion controlled by the vertical magnet 15 and rotary motion controlled by the rotary magnet 16. The usual side switch.

comprising the Wipers 17, 18, 19 and 20, is

controlled by the private" magnet 21. in a well-known manner. lhe usual magnet restoring the mechanism to nornial position is represented at 96. The usual vertical and rotary line relays are reprei seated 24 and :23, respectively. The selector i (Fig. 2) is similar in construction to selector E, the circuits being changed, however, in order to adapt it to operate in a twoovire system, as fully disclosed in British patent to G. Martin, No. 1419 of 1910.

release.

device for the first itl,-.

The connector 1. is of the general type of connector switches disclosed in United States Letters Patent No. 815,176, granted lliarch 13, 1906, to Keith, Erickson and Erickson,

' the circuits being modified, however, in order to operate in a two-wire system, as shown in thesaid Martin British patent... Likewise, the line switch C and the substation A are specially adapted for operation in such a two-wire system.

The repeater F (Fig. l) is the connecting link between the three-wire system and the two-Wire system, this repeater being adapted to receive impulses of the character which are produced by the three-wire substation A and to transform them into impulses of the proper character for operating the switches of the two-wire system represented in Fig. 2. This repeater comprises the usual rcrtical and rotar Y line relays 26 and 27. The relay 28 is a slow acting relay-"that is, av relay which deenergizes slowly after the energizing current is withdrawn from it, The proper operation of this relay may be obtained by securing a ring oi copper or other conducting material around one end ol. the

1 core. The winding the relay :29 is simply connected in a local circuit with one winding 30 of a doublewound induction coil The relation of the windings 31 and. 30 of the coil 32 ls-sueh that whenever a. circuit is closed through the winding 31, current is set up in the wiudiu 30 induction, which cur-- rent flows throw the winding of the relay 29 and is of suilicieut'strength to momentarily energize said relay. will thus be seen that an i ipulse is transmitted to the relay 29 each .ie tl J circuit or the Winding 31 is closed, and that the impulse received by the relay 29 is only momentary, even though the circuit of the winding be closed for a considerable length of the. The talking circuit through the repeater is divided into two sections which are inductively connected by the condensers 166 and 107. i

In order .to give a complete undelstanding, of any invention. the operations by; which the calling subscriber A. obtains nection with the called subscriber A. will now be explained. Since the construction. and operation of the s itching apparatus disclosed herein isin general well known in the art, and'is fully described in the publications hereinabove referred to, it not thought necessary to describe its operation in detail. Sufiicient description will be given to enable my invention to be -coi'npletely understood.

It Will-be assumed that the number of the called substation A. is 2220'. i i 'hen the call-- 111g subscriber, after removing his rec cr from the switch hook, operates his calling nary engagement of the substa n iuuiiulse springs 8 and 10 upon the initial movement of the dial transmits an impulse of current e preliuiithrough the springs 42. relay over a circuit extending from grotmd (.i' at the, substation through said impulse springs and over the line conductor 3 and through the trip magnet 1H ot the line switch t to battery 1%. The magnet 'S-l, upon cl'tcrgizing, releases the plunger ol' the line switch. allowing it to enter its bank, whereby the line conductors 2-5?) and are extended through the line switch hank stnings to and 37 and 38 and 3-) to the first selector l'l. After the line switch C has operated, its master switch I) operates in a well-known manner to advance the plungers of the remaining line switches of the group to which the switch t belongs to an idle trunl: line. After the connection has thus been extended to the first selector E, two impulses are transmitted over a circuit extending from ground G at the substation A through the ground post and the vertical impulse spring T. vertical line conductor 35, springs 38 and 35h side switch wiper 1'7 and the vertical line relay 2% of the first selector E to battery it The selector}? operatesin response to these two impulses through its vertical relay to cause the vertical magnet to raise the switch shaft and wipers 12, 13 and 14 two steps to a position opposite the second row or level of bank contacts, which contacts are assumed to be the'terminals of trunk lines leading through the repeaters I to the twowire system shown. in Fi After the two impulses are delivered over the vertical line one more impulse is transmitted over the rotary line 33 and througl'i the selector rotary line relay '23 to battery. This impulse through the relay 23 causes the private magnet 21 to operate in the usual manner to advance the side switch from first to second position, whereupon the rotary magnet it operates to rotate the. switch sha't't until the. wipers 12, 13 and 14: engage the contacts ol an idle trunk lino, whereupon the sideswitch passes to third position, thereby con'iplcting the connection" between the calling substation. and an idle repeater F. nec-tion is thus extended to the repeater. it is protected from seizure by any other selector E by a guarding potential which extends vfrom ground G through the side switch wiper of the selector, relay ll) and lhc private wiper 14 to all the selector private bank contacts of the. seized trunk. Front the wiper H- a circuit also extends through the private bank contact through the lwo windings of the relay 41 in the repeater in series to the balcry B. The relay 4] iscncrgized by the closure of this circuit. but it possesses a sullicicntly high resistance to prevent sulticicnt current from llowing to operatively energize the relay ll) of the selector E. The relay l1. upon energizing coup plctes a circuit extending from ground (lc l1) Ilttl the springs 'l-l' to the battery l3, and also closes a bridge across the trunk conductors l? and lo. whereby an energizing circuit is completed tor the line relay l7 ol' the selector H. The complete circuit ol' the relay -lT extends l'ront ground ti through the lowcr winding of said relay. side switch wiper l conductor 'll'aisprings l9 and 55 of the relays 4;) and 21' in'parallcl. springs 3t) impedance coil 51. condu tor 45. side switch wiper 52 and the upper winding of the relay l? to battery B. The relay 47, upon energizing. completes an energizing circuit through the relay B-l. The apparatus is now in position to receive the impulses tor the second digit 2. which impulses will be repeated by the repeater I from the calling substation to the selector Il.

\Vhen the calling device at the substation A is operated for the second digit 2, one impulse is transmitted over the rotary line 33). followed by two impulses over the vertical line 35, and then one more over the rotary line in the usual manner. The rotary impulses for this digit. as well as for all succecding digits, are i'unctionlcss. These impulses over the rotary'line pass through the rotary line relay 27 of the repeater F and the relay to battery B. These relays are momentarily energized by these impulses. The rotary line ti'elay 27. when energized, closes a circuitv extending from ground G" through winding 31 ot coil 32. springs 57 and 94' and righy hand winding of coil 41 to battery B. The energization of winding 31 induces a currcht in winding 23th which is included in a local circuit with relay 29. Relay 29 thereupon energizes and opens the contact of springs it, thereby opening the energizing circuit of relay l3. Relay 43. upon deiinergizing, opc hs the contact of springs 15). The springs 49, however, are in multiple with springs and therefore their operation is without ellti ct at this time. The

vertical impulses for the second digit 2 pass fl'Olll the substation ground over the verltcal line condtmtor and through the vertical lmerclay 2t) and the relay 28 in the ropeatcn "to battery. The engagcmentl ol the springs 56 and 57, upon the onergization oi the relay 26. completes a circuit extending from ground G through the winding 31 ol the coil 32 and the springs 57 and 56 to battery B. This closure of the circuit through the winding 31 induces acurrent in the winding 30 which llows through the relay 2!), thereby momentarily energizing the latter relay, which operates to open the circuit of the relay 43 at the springs 44. It will thus be seen that a momentary impulseis transmit* ted through the relay Zileach time an impulse is transmitted from the substation through the \erli ad line relay 26. In its energized posilion the relay 29 opens the circuit ol the relay 43, which allows the springs 15 to be separated, while, at the same time the springs are opened by the encr- Q1: .x riu gization of the relay 26, Waerehy the "ont-inuity of the bridge across the izwcsrire trunk conductors 45 and i6 is-opezied in mentarily each time an impulse is ire'ismitted from the substation threugh the rele 26. The relay 28, which inchuiccl the energizing; circuit of the vertical 26, is a slow acting relay elicl e F energized upon the receipt or he meal acsti pulse and remains in its eiierg' continuously until after the lash im delivered. In its energized pceicicn lay 28 opens the talking circuis repeater and short-circuits the coil 51 through the springs 58 i as to remove it from the qyeraiing of the line relay i? of the sclccier H 2). Each time the bridge is opened at the springs 55 l relay 4c? of -the selector H ch inenterily. The slow acting relay i cices not denergize during the momentary ruptions of its circuit by the relay 4'2} and therefore, each time the line rel?" is energized, a circuit: is closed throu'l vertical magnet 59 in I series with acting relay (50. Since the digit es the vertical magnetepereses to switch shaft and wiper two steps. acting relay 60 operates in respeiis 1 impulses to close the circuit of i;

the last impulse is delivered, when bl vate magnet (ienergizes and side switch to pass to second, pos j upon the rotary magnet 82 euro malice rotates the Wipers step h sivcp iii and well-known manner onto in an idle trunk, whereupon he passes to third posillou mui errlc nection threugh wipers 55L the shalt Wipers 53 and l in hr he'sconies cu c l. 'v hen connection 15 thus iii-(tended lo connector, its line relay gizcd in the same man in 'Whic i the relay 47 of the selec-loi first became egized and closes uv circuit through the lay 66.

\Vhen the calling subscriber op culling device for iahe digit I repeater l opcraics in. the same may: for the previous digit to illmlill lil'i I the bridge across the trunk coiulue 1 end 46 twice, each time causing the of the connector E to ilc iiergize time the relay (55 cleiiiiergizes iii iespc the impulses for this (ligifi it. clos s a c from ground G through ihe re i, net 69 and the relay 70 inc hzu'ztetqv if two impulses are transmitted ore cuit, the vertical magnet cperzile the switch shaft and wipers i'swo s the slow ecting relay causes mag ict M 0 step the SW c; to second positien. liii "eccmi.

.rticiil line relay 2?: cf repeater,

s alter opereies in turn no momenta ri 1 the circuit of the connector en times. Each time the relay 65 rleiicigizaes iii resouse il a e impulses s a circuit through the rotary magnet he rcle filfl The relay 70 operates iihe ewiizch she'll. ten steps to carry were eni'g the cenhcts of ihe called. 2220, after which the private meg-' lei the influence cf the rele; 78

' tch to peas from see .o rezwliieg chi i position, 155 ci he in n the calh subs-trillions, as eutlineo, wings. The bhe line the .3 close! cm. is encrgizesl over a connector flireugh the side switch Wiper Y8 c wipcr 12A), mun: CQIRECe upon which s SSiJTl'lg and the Wll'ldlhg 77 so batiery T e coouectien or ground. G with the ciaor private bank contacts of the called li' ver ii perticn of the circuit just traceii if Ides a, guarding potential for said cou- 1 to prevent a second connector from ohccnneclion with the same line While The engag ment of ifihc side i of the cm tor with its elOll contact point closes izhe cir- (l circuit interrupted rrupicr 82, so as subscriber confine My A the milking circui'i oi Elie celled sue-simian iii-nigger? across the line con- (rumors 81%- v the response oi the i soon thereafter as ilceuerfg zes, if it hepi the time, callefi eel with talking current over ,iflrjiilg i ifi lli ground G at me whi h iahc side switch Wiper the relay 86, rmger re The side switch wipsubscriber.

- gization of i om ground at the l the iiiupper winding of the relay 86 to the battery B. The relay 86 is energized by this talking current and by separating the springs 83 the circuit of the ringing relay 81 is opened.

It} will thus be seen that after the connection is completed with a two-wire substapon A, the ringing current is automaticalLy supplied to said line without any control of the calling subscriber, and is automatically cut off when the called subscriber answers. If, after calling the two-wire substation, the calling three-Wire subscriber should depress his push button 11. as he is required to'do when calling a three-wire subscriber, the circuit of the vertical line reiay 26 of the repeater F will be closed. The {relay 26 would operate in response to the 'closure of this circuit to open the bridge across'the two-wire trunk conductors 45 and 46 inflthe same manner as when digits are being called. However, since the relay 29 i is energized only momentarily, even when f the circuit or" the relay 26 is closed for a proat the callin longed period of time, the relay 43 will be deenergized only for an instant, and then return to its energized position and close the bridge across the conductors 45 and 46, even though the relay 26 remains energized. Thus it will be seen that the prolonged energizetion of the vertical line relay 26 of the repeater, by the pressing of the ringing button substation A, can do no more than transmit a momentary impulse to the connector line relay 65, which impulse endures only as long as the relay 29 in the repeater F remains energized. This short impulse does not cause the connector line relay 6:) to open the circuit of the slow acting release relay 66 long enough to cause the con nection to be released.

Afterthe conversation is completed, the connection is released by the hanging up of the receiver at the calling substation A.

As the switch hook at the substation A de-- scends when the receiver is hung up, the springs 91, 92 and 93 are momentarily forced into contact, whereby the vertical and rotary line conductors 35 and 33 are grounded simultaneously, thereby energizing both the vertical and rotary line relays 26 and 27 of the repeater F, The combined energization of these two relays completes a connection from the battery B through the springs 56, 57 and 94 to the common terminal of the two windings of the relay 41. This connection short-circuits the righthand winding of said relay 4:1 and thereby increases the current in the relay 40 of the selector E sullicieiitly to cause it to be operatively energized. The relay 40, upon energizingcloses the circuit of the release magnet 96. The magnet 96, upon energizing. closes the circuit of the release magnet 97 of the line switch C. The magnets 96 and 97, upon energizing, attract their armatures and hold them in readiness to IGlBilSt their respective switches, when their cir cuits are broken as a result of the deenergization of the repeater line relays when the switch hook at the substation has descended far enough to permit the springs 91., 92 and. 93 to separate. The release of the first selector E destroys the energizing circuit of the relay 41 of the repeater F, whereby the bridge across the trunk conductors 45 and 46 is broken and the connector line relay 65 is permitted to dei nergize permanently. The relay 65, uponde'c'nergizing, breaks the circuit of the connector release relay 66 and also the circuit of the release relay of the selector H, which circuit is maintained closed directly by the springs of the relay 65 after tlie side switch. wiper 98 of the connector reaches third position. The relays 66 and 5-1, upon deiinergizing, close the circuits of their respective release magnets 99 and 100 which, upon energizing, immediately restore the mechanisms of their respective switches to normal position; and when the switch shafts reach their lowest positions, the circuits of the release magnets are opened at the springs 101 and 102. respectively.

It will be seen that I have provided a very eflicieut form of three to two wire repeater, and one in which there is no danger of-the two-wire switches being released by the prolonged grounding of the vertical line by a subscriber.

While I have illustrated one particular embodiment of my invention and have shown this in connection with an automatic telephone system of a particular type, it is to be understood that I do not wish to be limited to the exact construction shown and described, and that. furthermore. my repeater is adapted for use in connection with many other automatic telephone systems or semi-automatic SYStGIIlS, as will be readily understood.

What. -I claim as my invention is 1. In a telephone system, an automatic switch, a repeater. means for transmitting a plurality of momentary impulses to said repeater, means controlled by said repeater for repeating a corresponding series of momentary impulses to said switch. means for transmitting a prolonged impulse to said repeater, and means controlled by said repeater l transmitting a momentary impulse in response to said prolonged impulse.

2. In a telephone system. a trunk line. a repeater in said trunk for controlling a bridge across the same, means controlled hy said repeater in response to a plurality of momentary impulses for momentarily opening said bridge a corresponding number of times. and means controlled by said repeater in response to a prolonged impulse for momentarily opening said bridge a single time.

telephone system, a trunk line, a repeater in said trunk, means for transmitting impulses to said repeaterover one side of said trunk and ground, means controlled by said repeater forrepeating said impulses over two sides of said t unk in. series, means for transmitting a prolonged im pulse over one side of said trunk, and means controlled by said'repeater for transmitting a momentary impulse over two sides of the trunk in series in response to said prolonged impulse.

in a telephone system, a trunk line, a repeater in said trunk comprising a line relay, means for transmitting a plurality of impulses eve: one side of said trunk and ground through said line relay, means con.- trolled by said line relay for repeating said impulses over two sides of said trunk line in series, means for transmitting a proiinpulse over one side of said trunk to said repeater, and means controlled by, said reoeater for transmitting a momentary impulse over two sides of said trunk linein response to said prolonged impulse.

5. a tel phone system, a trunk line, a repeater in said 7 alt, a bridge across said trunk, a line role for repeater, means for operating said line relay by impulses transmitted over one side of said trunkand grounc, a second relay, means controlled by the operation oi line relay for inducing; impulses tlnsougli said second relay, and means control 3. in a t ie jnone system,a trunk line, a, repeater in said trunk, a bllCifZfi across said in unit line, a line relay for said repeater, a, second relay, .118 for transmitting aplu rali 'of momentary impulses over, one side of said trunk and .JI'Ollnd to operate said line relay, means contro led cy the operation of saiddine relay for momentarily energizing. .id second relay, means controlled by the energisation of saidsecond relayfor. opening said bridge. and means for trans muting a prolonged impulse through said.

line relay, said yrolonged energization of said line relay adapted to momentarilyenergize said second. rein to thereby again momentarily open said bridge.

7. in a .tel repeater in aid trunk, a bridge across said trunk, a pair parallel connections for controlling the continuity of said bridge, a. line relay for said repeater for controlling on of said parallel connections, and a sec 1 elay controlled by induced impulses said line relay for controlling the other so id connections. Q

re eater in. trunk, means for seizing liridge across said trunk osed when said trunk is seized, a pair.- of parallel connections in said d by said second relayi'or;

eplione system, a trunk line, a

in telephone system, a trunk line, a

nsenoso bridge for controlling the continuity of the same, a line relay adapted to be energized by nnpulses transmitted over said trunk for -co1itrolling one of said parallel connections,

said line and parand a. second relay controlled by induced impulses by said line relay for coi'itrolling the other. of said parallel connections.

10. in a telephone system, a trunk line, a repeater in said trunk, a bridge said trunk, a pair of parallel eonnectionsin said bridge controlling the continuity of the same, a line relay for controlling one of saidco' ciions, a second relay controlling tlie .li'iier of said connections and closing; said connections when energized, to energizing said line .relayby a prolonged impulse to open one of said parallel connections, and means controlled by said pro-- longed 'energization for inon'ientarily deencrgizing the other of said relays to there by momentarily open said bridge.

11. In a telephone system, a trunk line, repeater in said trunk, a relay in said repeater, and means tor operating said relay by induced impulses, said repeater adapted to receive impulses over one side of the trunk and ground and to repeat inipulseszoyer two sides of the trunk in series in a telephone system, a trunk line, an automatic gn-ogressively movable switch associated with said trunk line, abridge across said trunk line, means for transmit ting impulses in said bridge for operating" said switch, said means comprising a relay,

and means for-operating said relay oynn duced impulses. I

13. In a telephone sys tion of an automaticproggiessivel movalole switch, trunk lines,an electromagnetic impulse reproducer for operating the switcli to connect with one oi said twink lines, and means for operating said reproducei: by duced impulses for tile purpose forth.

14.- ln a. telephone system, the combination with a trunk line divided into two sections, of a repeater for repeating impulses iron: one section to the other, said repeater including means responsive to impulses of variable lengths received over one section a trunk line divides into two in, the combine.

tions, of a repeater for repeating impulses from one section to the other, said repeater including a relay responsive to impulses of variable duration received over one section of said trunk, an induction coil energized responsive to said relay, and a second relay controlled by the induced current from said coil for transmitting impulses of uniform duration over the other section of said trunk.

16. In a telephone system, the con1bination with a trunk line divided into two sec tions, of a repeater for repeating impulses from one section to the other, said repeater including a relay responsive to impulses of variable duration received over one section of said trunk, and a second relay controlled byisaid first relay for transmitting impulses of uniform duration, over the other section or? said trunk.

{17. In a telephone system, the combination with a trunk line divided into two sections. of a repeater for repeating impulses from one section to the other, said repeater including a relay responsive to impulses of variable duration received over one section of said trunk, an induction coil comprising a pair of windings, one of said windings being controlled by said relay for the purpose of inducing a current in the other of said windings, and a second relay controlled by said induced current for transmitting impulses of uniform duration over the other section of said trunk.

18. In a telephone system, a relay, an automatic progressively movable trunking switch controlled by said relay, and means for operating said relay by induced impulses.

Signed by me at Sioux City, Woodbury county, Iowa, this 19 day of June, 1912.

WILLIAM A. LONG.

Witnesses:

C. R. ME'roALFa, E. B. LYS'I'ER. 

